Electron camera tube



Feb. 13, 1945. A. Dt HULBERT 2,369,569

ELECTRON CAMERA TUBE Filed May 50, 1942 vl/EN TOR A. D. HULBE R7' A 7'TORNEV Patented Feb. 13, 1945 UNITED STATES' PATENT OFFICE 2,369,569ELECTRON'CAMERA TUBE Arthur D. Hulbert, Flushing, N. Y., assignox` toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application May 30, 1942, Serial No. 445,243

tial which is somewhat greater than that of the Claims.

This invention relates to.electron optical devices and more specificallyto electronl camera tube arrangements for television.

Many forms of electron camera tubes employing storage are known in theprior art, including some incorporating a target member of the twosidedmosaic type, that is, a target which is adapted to have radiations froman object applied to one side and a moving scanning beam of electronsapplied to the other side.

It is a principal object of the present invention to provide anarrangement including an improved electron'camera tube of the typeincorporating a two-sided mosaic target.

In accordance with the invention there is provided a television cameratube which, because of suitable potentials applied to various electrodestherein, has at all times a saturated collecting eld for photoelectronsbetween the light sensitive particles on one face of the two-sidedmosaic target anda collecting electrode, and provides for completeelectric eld isolation of each light sensitive particle so that nocharge transfers of any kind can occur among the particles.

In accordance with one aspect of the invention, there is provided anovel cathode ray television transmitter tube arrangement employing atwosided mosaic having a matrix which vis maintained at a negativepotential with respect to the col- -lecting electrodes for the secondaryelectrons and photoelectrons, respectively, emitted from said mosaic.

In accordance with a preferred embodiment, chosen by way of example toillustrate the principles of novelty of the present invention, anarrangement including a television camera tube is provided which tubecomprises an evacuated envelope enclosing means for generating a beam ofelectrons, a target for the beam, and two collecting electrodes onopposite sides of the target. The mosaic target comprises a conductingmatrix having a plurality of apertures therein, an insulated lamentbeing provided for each aperture. The matrix is placed at a potentialwhich is negative with respect to both collecting electrodes. The end ofeach filament remote from the electron beam is photosensitized. An imageof an object is projected upon the photosensitized side of the targetand the other side is scanned with the beam of electrons. The ends ofthe lament are made iiush with the matrix on both sides of the target.

The principle of operation of this tube is as follows: While it is underthe scanning beam spot, each illament attains an equilibrium potenmatrixbut still considerably less than that of the collecting electrode on theelectron beam side of the target, which collecting electrode may be theiinal anode of the electron gun utilized for generating the scanningbeam of electrons. Between successive scans each filament acquires apositive charge through the loss of photoelectrons to the photoelectroncollector electrode and its potential ris'es above the equilibriumpotential at a rate determined by the amount of light falling upon it.The matrix is thus always negative with respect to every filament, asevery filament is at or slightly above the equilibrium potential at alltimes. Being thus completely surrounded by a negative potential barrier,the secondary and photoelectrons from one filament are unableto passover this barrier to any other filament; they must either continue on tothe final anode of the gun or to the collector electrode for the'photoelectrons, respectively, orreturn to the lament from which theystarted. On the photosensitive side of the mosaic, suicient collectingi'leld is provided to draw every photoelectron to its collectorelectrode. On the scanning side of the mosaic, however, the equilibriumpotential that the filaments assume While under the scanning beam issuchthat (at equilibrium) only as many secondary electrons havesuiiicient energy to reach the iinal anode as there are primariesarriving in the beam and the remainder of the secondaries have toolittle energy to reach the nal anode and fall back inside the potentialbarrier to the filament from Vwhich they were emitted. The variation inthe current to the nal anode constitutes the video signal current.`Because the tube provides for complete collection of every photoelectronand prevents substantially all redistribution losses, this tube has amaximum signal output.

In the tube of this invention, the matrix has a dual role i'n that itnot only provides a barrier grid action on both sides of themosaic butalso serves as the signal plate at the same time. In the ordinary tubeof this general type, one screen is used for the signal plate While aseparate screen is used to provide a barrier grid action on one side ofthe mosaic facing'the scanning gun only. The combining of these func--lforming a part thereof in which:

Fig. 1 is a schematic representation of a cathode ray tube of thisinvention and certain of its associated circuits;

Fig. 2 is an enlarged cross-sectional view of a portion of the mosaictarget of Fig. 1 taken in a plane parallel to the surface upon which thescanning electrons impinge.

Fig. I3 is an enlarged cross-sectional view taken in a plane indicatedby line 3--3 in Fig. 2.

Referring more particularly to the drawing, Fig. 1 discloses, by way ofexample to illustrate the principles of this invention, a cathode raytelevision transmitter tube I employing a twosided mosaic II togetherwith certain of its associated circuit connections. The tube I0comprises an evacuated envelope I2 enclosing the mosaic target I I, anelectron gun I3 for generating, focusing and accelerating a beam ofelectrons towards this target, a collecting electrode I4 forphotoelectrons emitted from the target when radiations from an object oreld of View are applied to the side thereof remote from the beam ofelectrons by means of a suitable optical system represented by the lensI5, and two sets of lmagnetic coils I6, I6 and I1, I'I for causing thebeam of electrons to scan every elemental area in turn of a field ofview on the mosaic target II.

The electron gun I3 preferably comprises a cathode 20, a modulatingelectrode or member 2 I. a first anode member 22, and a second and finalanode member comprising a cylindrical member 23 and a coating 24 ofconducting material on the inside walls of the envelope I2 extendingfrom the region of the cylinder 23 to the region of the mosaic targetII. The collecting electrode I4 for the photoelectrons emitted from theleft-hand side of the mosaic target II in Fig. 1 also preferablycomprises a conducting coating (in the form of a ring) on the innerwalls of the envelope I2. The coatings I4 and 24 are separated andelectrically isolated from one another.

The modulating electrode 2| is placed at any suitable negative potentialwith respect to the potential of the cathode by means of an adjustablesource 30; the first anode 22 and the final anode 23, 24 are placed atappropriate positive potentials with respect to the cathode 20 by meansof the source 3|. An inner terminal of this source is connected directlyto the anode member 22 while the positive vterminal of the source 3| isconnected through a signal resistor 32 to the nal anode members 23, 24.The negative terminal of the source 3| is connected to the cathode 20.The potentials applied to the various electrode members are such that abeam of focused electrons strikes the target II and this beam isdeflected over a suitable field or raster thereon by means' ofappropriate currents passed through the deilecting coils I6, I 6 andI'I, I1 by means of suitable sweep circuits (not shown). Any sweepcircuits suitable for operation with magnetic defiecting coils for acathode ray tube are satisfactory for the purpose.

Reference will now be made to Figs. 2 and 3 which show enlarged portionsof the mosaic target II. Fig. 2 is a cross-sectional view taken in aplane parallel to the large surfaces of the mosaic target while Fig. 3is a cross-sectional view taken in a plane indicated by the line 3-3 inFig. 2. The mosaic target II preferably comprises a matrix 40 ofconducting material having a plurality of apertures therein which arefilled with filaments 4I having insulated coatings 42 around them. Thematrix 40 is placed at a negative potential with respect to theconducting coating 24 and the cylinder 23 by means of source 33 and at anegative potential with respect to the collecting electrode I4 by meansof source 34. The left-hand ends of the filament 4I (in Figs. 1 and 3)are photosensitized in any manner known in the art. Both ends of thefilament are made flush with the corresponding surfaces of the matrix40. This feature simplifies the manufacture of the mosaic target I I.

'I'he target II may be made in a number of ways. One example of asatisfactory way of making this target is known as the wire bundlemethod. To make a two-sided mosaic by this methody wire of very smalldiameter is first coated with a thin uniform layer of a suitabledielectric material and then coated with a very thin metallic layer.This forms a miniature cable which can then be reeled up (perhaps withfurther metal being used to ll the spaces between the cables) in such away that after it has been bound together and a thin slab has beenformed by cuts perpendicular to the direction of the wires, the desiredstructure will have been formed. As a specific example of one way ofperforming this method, aluminum wire can be anodically oxidized toinsulate it, and then coated with a thin layer of Hanovia silversuspension and baked. Hanovia silver is a suspension of silver and smallamounts of other metals such as a-ntimony in oil. While the resultingminiature cable is being layer-wound around a thin fiat board, a tinfoilmade of an alloy of about per cent aluminum and 20 per cent silver iswound between each layer. When the cross section of the coil has reachedthe correct dimensions, as for example about 5 inches wide and 2 inchesdeep, and after the flat board has been removed, the coil is squeezedtogether eliminating the space where the board has been. This assemblageis then baked to a temperature which is sufficient to melt the foil butwhich is below the melting temperature of the aluminum wire. Thus thefoil is fused into a matrix. If desirable, pressure is applied at thesame time to squeeze the wires together and to make sure that the matrixcompletely fills every interstice. Slabs, perhaps of the order of 1Ainch thick, are then formed by cuts perpendicular to the wires andsilver is electroplated upon the exposed wire ends and the exposedmatrix on one side of the tube. If necessary to get the silver to stick,a preliminary plating of nickel may be found necessary. After mountingthe slab in the tube the usual processes of oxidation and treatment withcaesium are used to produce photosensitivty on the lefthand side of themosaic as shown in Figs. 1 and 3. The photosensitivity of the matrix 40makes possible control of the average intensity at each instant of thereproduced image at a suitable receiver. The current flowing in the leadWire 35 connected to the matrix 40 is directly proportional to theaverage intensity at each instant of the object or field of viewprojected upon the left-hand side of the mosaic target II by means ofthe lens system I5. By means familiar to the art, the variations of thiscurrent can be transmitted along with the video signal. The amplitude ofthe blanking pulse can be controlled by this current.

The principle of operation of the tube shown in Fig. 1 is as follows:Radiations from an object or field of view are projected upon theleft-hand side of the mosaic target II by means of the lens system I5.The beam of electrons generated by narily in tubes of the two-sidedmosaic type. one

the electron gun i3 is deflected vover a field of the mosaic targetcorresponding to the area covered by the radiations from the object bymeans of defiecting currents supplied to the deiiecting coils I6, I6 andI1, Il. While it is under the scanning beam spot, each filament 4Iattains an equilibrium potentia1 somewhat greater than that of thematrix 40 but still considerably less than that of the final anode 23,24 of the scanning gun. The matrix 40 is placed'at a negative potentialwith respect to the final anode 23, 24 and at a constant potential withrespect to ground by means of the source 33. The ends of the filaments,however, are not connected to any source of constant potential and thepotential of the filaments rises due to the secondary electrons givenoff from the filaments 4| by the impingement of the primary electronsfrom the gun I3 thereon. Between scans, each filament 4I acquires apositive charge through the loss of photoelectrons from the coating 43to the collecting electrode i4 for the photoelectrons, which is placedat a positive potential with respect to the matrix 40 by means of thesource 34. The potential of each filament 4I thus rises above theequilibrium potential at a rate determined by the amount of lightfalling upon it from a corresponding elemental area of the object or eldof view O. It follows then that every element is at or slightly abovethe equilibrium potential at all times and this being so the matrix isalways negative with respect to every filament. Being thus completelysurrounded by a negative potential barrier, secondary electrons andphotoelectrons from one filament are unable to pass over this barrier toany other filament; they must either continue on to the second anode(that is, the collecting electrode 24) or to the collector electrode idfor the photoelectrons, respectively, or return to the filament fromwhich they started. On the photosensitive (left-hand) side of themosaic, suicient collecting field is provided to draw everyphotoelectron to the collector electrode I4. On the primary beam side ofthe mosaic (the right-hand side in Figs. 1 and 3) however, the

- equilibrium potential at the filament 4I while under the scanning beamis such that (at equilibrium) only as many secondaries have suicientenergy to reach the second or final anode 24 as there are primariesarriving in the beam and the remainder of the secondaries have toolittle energy to reach the final anode 24 and fall back inside thepotential barrier to the filament from which they were emitted. Duringeach scanning sequence, the scanning beam from the gun I3 replacessuccessively at each filament 4I the number of photoelectrons thatfilament has lost since the previous scan, and the instantaneous totalnumber of secondary electrons going to the final anode 24 is thereforediminished by the number of replacement electrons being taken by thefilament 4| being scanned at that instant. The variation in this finalanode current constitutes the video signal current, and this currentpasses through the signal resistor 32 which is connected to the inputcircuit of an amplifier in a manner well known in the art. Because itprovides for a complete collection of every photoelectron and preventssubstantially all redistribution losses, the

tube of this invention has a maximum signal out- I screen is used forthe signal plate while a separate screen is used to provide a barriergrid action on the one side ofthe mosaic facing the scanning gun only.Combining these functions in the matrix simplifies the mechanical designof the mosaic structure. Preferably, as pointed out above the ends ofthe filaments are flush with the respective surfaces of the matrix. Thisis possible in accordance with this invention because no specialindentations or protuberances are neces,- sary to produce the barrieraction.

Various modifications may be mada in the embodiment described aboveWithout departing from the spirit of the invention, the scope of whichis indicated by the appended claims.

What is claimed is:

1. lAn electron camera tube arrangement comprising an envelope enclosingmeans for generating a. beam of electrons, a target for said beamcomprising a matrix of conducting material having a plurality ofinsulated conducting elements therein, said conducting elements being sopositioned that each has an exposed face on each side of the target, aphotosensitive coating on the face of each element remote from the beam,collecting means for secondary electrons generated when said beamimpacts said target, a collecting electrode for photoelectrons emittedfrom the photosensitive portions of said element. and means for placingsaid matrix at a xed potential which is at all times negative withrespect to that of said collecting means and said collecting electrode.

' 2. An electron camera tube arrangement comprising an envelopeenclosing means for generating a beam of electrons, a target for saidbeam comprising a. conducting member having a mul'-y tiplicity ofapertures therein, an insulated conducting element in each aperture sopositioned that each element has an exposed face on each side of thetarget, said faces being substantially iiush with the surfaces of saidconducting member, a photosensitivel coating on the face of each elementremote from the beam, collecting means for secondary electrons generatedwhen said beam impacts said target` a collecting electrode forphotoelectrons emitted from the photosensitive portions of said element,and means for placing said conducting member at a xed potential which isat al1 times negative with respect to that of said collecting means andsaid collecting electrode.

3. An electron camera tube arrangement comprising an envelope enclosingmeans for generating a beam of electrons, a target for said beamcomprising a conducting member having a multiplicity of aperturestherein, an insulated conducting element in each aperture so positionedthat each element has an `exposed face on each side of the target, saidfaces being substantially flush with the surfaces of said conductingmember, a photosensitive coating on the face of each element remote fromthe beam collecting means for secondary electrons generated when saidbeam impacts said target, a collecting electrode for photoelectronsemitted from the photosensitive portions of said element, and means forplacing said conducting member at a potential which is xed with respectto that of the cathode of the beam generating means and which is at alltimes negative with respect to that of said collecting means and saidcollecting electrode.

4. The combination of elements as in claim 1 in which the exposed facesof said elements are substantially ilush with the surfaces of saidcomprising a conducting member having a multiplicity of insulatedconducting elements therethrough, said elements being so positioned thateach one of them has an exposed face on each side of the conductingmember, a photosensitive coating on the face of each element remote fromthe beam generating means, collecting means for secondary electronsgenerated when said beam impacts said target, a collecting electrode forphotoelectrons emitted from the photosensitive portions of saidelements, means for setting up an electric eld between saidphotosensitive portions of said elements and said collecting electrodeto cause substantially all of said photoelectrons to be collectedthereby, and means for setting up an electric eld between the conductingelements and Said conducting member so that secondary electrons areprevented from being emitted from one element to another element.

6. In combination, a target for electrons comprising a rsi; conductingmember, insulating material disposed about said member in such a waythat two faces of said member at opposite ends thereof are leftuninsulated, a second member of conducting material contiguous to saidinsulating material, a photosensitive surface for one of said faces, aphotoelectron collecting electrode adjacent said photosensitive surfacefor receiving photoelectrons emitted therefrom, means for generating abeam of electrons and for periodically directing it to the other of saidtwo faces, a collecting member for secondary electrons emitted from saidother face when impacted by said beam, said emission of secondaryelectrons and of photoelectrons causing said first conducting member tovary in potential from an equilibrium Value when the beam is in contacttherewith to values positive with respect to said equilibrium value whenthe beam is not in contact therewith and when radiations are applied tosaid photosensitive surface, and means for continuously maintaining saidsecond member at a negative potential with respect to said equilibriumvalue.

'7. In combination, a target for an electron beam comprising a matrix ofconducting material having a plurality of insulating conductingelements, said conducting elements being so positioned that each has anexposed face on each side of the target, a photosensitive coating on thefaceof each element remote from the beam, means for receiving secondaryelectrons generejacs.

ated when said beam impacta' the target, a collecting electrode forphotoelectrons emitted from the photosensitive portions of said element,said emission of secondary electfons and of photoelectrons causing eachof said conducting elements to vary in potentia /from an equilibriumvalue which is substanti ly the same for all elements and which eachelement assumes when the beam is in contact therewith to a valuepositive with respect to said equilibrium value when the beam is not incontact therewith and when radiations are applied to said photosensitivesurface, and means for continuously maintaining said matrix at anegative potential with respect to said equilibrium potential.

8. In combination, a target for electrons comprising an array ofinsulated parallel conducting members each having two uninsulated ends,metallic material forming a matrix around said insulated members, meansfor forming a beam of electrons, means for causing said beam to scan aface of said target including an end of each conducting member wherebyeach member is driven to an equilibrium potential by the passage of thebeam over its said end, means for producing electron emission from theother of said ends of some at least of said conducting members, saidemission from a member causing the potential thereof to become morepositive than said equilibrium potential during the period of time it isnot contacted by said beam, and means for maintaining said matrix at alltimes negative with respect to said equilibrium potential.

9. In combination, a target for electrons comprising an array ofconducting members, metallic material between but insulated fromadjacent ones of said members, all of said metallic material beingmaintained at the same potential, means for forming a beamof electrons,means for causing said'beam to scan a face of said target including anend of each conducting member whereby each member is driven to anequilibrium potential, means for producing electron emission from theother end of some at least of said conducting members, said emissionfrom a member causing the potential thereof to become more positive thansaid equilibrium potential during the periods of time it is notcontacted by said beam, and means for maintaining all of said metallicmaterial at all times negative with respect to said equilibriumpotential.

10. The combination of elements as in claim 9 in which said other end ofeach of said conducting members is coated with photosensitive material.

ARTHUR D. HULBERT.

